Clinical depression, including Major Depressive Disorder (“MDD”), is a significant public health problem. Major depression is associated with a significantly increased risk of developing serious medical illnesses such as diabetes, cardiovascular disease, immune impairments (“immunosenescence”), stroke, dementia, osteoporosis, diabetes and metabolic syndrome, and of dying significantly earlier (even after accounting for socio-demographic factors, suicide and risk factors such as smoking, alcohol and physical illness). See, e.g., Brown E S, Varghese F P, McEwen B S, Biol Psychiatry, 55(1):1-9 (2004); Musselman D L, Evans D L, Nemeroff C B, Archives of General Psychiatry, 55(7):580-592 (1998); McCusker J et al., Gen Hosp Psychiatry, 29(4):340-348 (2007); Irwin M R, Miller A H, Brain, Behavior, and Immunity, 21(4):374-383 (2007); Godbout J P, Johnson R W, Neurologic Clinics, 24(3):521-538 (2006)), (Arfken C L, Lichtenberg P A, Tancer M E, The Journals of Gerontology, 54(3):M152-156 (1999); Schulz Ret al., Archives of Internal Medicine, 160(12):1761-1768 (2000); Evans D L et al., Biol Psychiatry, 58(3):175-189 (2005); Gump B B et al., Stroke, 36(1):98-102 (2005); Rapp M A et al., Am J Geriatr Psychiatry, 16(10):844-852 (2008)).
Intensive research has been aimed at characterizing the pathophysiology of major depression on a cellular and molecular level. See, e.g., Duman R S et al., Archives of General Psychiatry, 54(7):597-606 (July 1997); Manji H K and Gottesman, II, Sci STKE, 207:pe49 (2003). However, there is currently no established biological or clinical test that can predict who is likely to develop depression. Additionally, although antidepressant medications and/or psychotherapy can be efficacious in treating depression, it is often inadequately treated and many patients fail to respond or continue to experience residual symptoms after treatment. Torpey D C and Klein D N, Current Psychiatry Reports, 10:458-464 (2008).
Therefore, there is a need in the field to develop methods for predicting whether a person is likely to develop depression, or if a person has been diagnosed with depression, whether that person is likely to respond to an anti-depressant treatment. The present invention addresses this need and others.